SOLAR SI-II LINE RATIOS FROM THE HIGH-RESOLUTION TELESCOPE AND SPECTROGRAPH

New calculations of electron-impact excitation rates for allowed transitions in Si ii are used to derive theoretical emission-line ratios involving the 3s(2)3p 2P(o)-3s(2)3d 2D, 3s(2)3p 2P(o)-3s3p2 2S, and 3s(2)3p 2P(o)-3s(2)4s 2S multiplets near 1262, 1306, and 1530 angstrom, respectively. A comparison of these line ratios with observational data from a quiet solar region, a sunspot, and an active region, obtained with the High-Resolution Telescope and Spectrograph on board a sounding rocket flight reveals that the 1530 angstrom multiplet is optically thick, which is consistent with a calculation of the optical depth of these lines through a model atmosphere. However, the 1262 and 1306 angstrom multiplets appear to be effectively optically thin. The average discrepancy between the theoretical and observed ratios is congruent-to 40%, which may not be significant, since the estimated uncertainties in both the calculated and experimental data are approximately 30%.